Motors can be used in boreholes to carry out many tasks, including operating hydraulic motors, rotating coring tool hole cutting saws, and opening/closing caliper arms. When powered near the end of a long cable, the voltage drop across the wires carrying current to the motor can be significant, since motors may use current in proportion to the mechanical loads they support. Thus, abruptly changing mechanical loads may result in correspondingly abrupt changes in supply voltage, both to the motor, and to instrumentation powered by, or derived from, the same supply.
Generally, shunt regulators may be used to help regulate downhole supply voltages as motor loads change. However, such shunt regulators may operate to cause unwanted heating near the area in the downhole tool where shunting occurs.